1. Field of the Invention
This invention relates to a writable recording medium, and particularly to a method and apparatus for performing a recording of data for an optical recording medium recorded with a support signal such as a wobbling signal which is used to record the data.
2. Description of the Related Art
Nowadays, an optical recording medium prevails in recording media for recording an information such as video and audio information. A write-once disc, such as CD-ROM, DVD-ROM, etc., and a write-once read-many type of disc, such as CD-R, DVD-R are available for the optical recording medium in the market. Recently, there has been suggested a rewritable disc such as CD-RW(compact disc-rewritable), DVD-RW(digital versatile disc-rewritable), etc.
As shown in FIG. 1, the DVD-RAM is divided into a data area DA for recording a user data and a header area HA pre-formatted with an identification information. The data area DA and the header area HA exist alternately in the circumferential direction of the DVD-RAM. As shown in FIG. 1B, the data area DA is provided with a groove track 10 having a concave section and a land track 12 having a convex section. These groove and land tracks 10 and 12 exist alternately in the radial direction. Recording pits are defined along a center-line of the disc at each of the groove and land tracks 10 and 12 to record a user data. The recording pits 14 are produced by which the recording material changes over from a crystalline state into an amorphous state. An optical reflective rate of the recording pit is lower because the recording pit has the amorphous state. Also, a boundary side 18 of the groove and land tracks 10 and 12 is wobbled in a shape of sinusoidal-wave signal. A wobbling signal occupying a low frequency band is detected by changing a light quantity reflected by the wobbled boundary side 18 periodically. This wobbling signal is used to generate a channel clock for detecting data from a data signal occupying a high frequency.
To record user data on the disc, a data recording apparatus as shown FIG. 2 is used. The data recording apparatus includes a bit counter 20, a recording pulse generator 22, a light driver 24 and a laser diode 26 connected serially to an input line 21. The input line 21 receives a channel bit stream CBS as shown FIG. 3. The channel bit stream CBS is obtained by encoding the user data in such a manner that a total length of the recording pits in a constant length of unit recording region corresponds to 50% the length of the unit recording region. Therefore, in the channel bit stream, there are included a plurality of data having "0" or "1" which is continued by 3 to 11 times. In other words, the channel bit stream consists of a plurality of data each having length of "3T" to "11T". The bit counter 20 checks whether the data included in the channel bit stream CBS has the length of 3T to 11T, and generates a pulse having a specific logic in a period which "1" is continued. By the bit counter 20, the channel bit stream CBS is converted into a channel bit clock CBC having a shape of signal required by the disc, as shown FIG. 3. Intervals of high and low logic in the channel bit clock CBC have the length of the 3T to 11T. The recording pulse generator 22 converts the channel bit clock CBC into a shape of signal adapted to generate recording lights. To this end, a recording pulse train WPT as shown FIG. 3 is produced in the recording pulse generator 22. The light driver 24 supplies the laser diode 26 with a driving current in accordance with the recording pulse train WPT from the recording pulse generator 22. The laser diode 26 irradiates a laser beam on the disc by the driving current from the light driver 24. The laser beam forces the crystalline state of the disc to change into the amorphous state such that the recording pits are defined on the disc. As a result, the user data included in the channel bit stream CBS is recorded on the disc.
The recording pits defined on the disc are detected in a form of a radio frequency signal while at reproducing. This results from the fact that a light quantity reflected by the recording pit of the amorphous state is less than that reflected by the crystalline region. Also, the recording pits are recovered into a shape of a pulse train by means of a reconstructed signal detector included in an optical disc reproducing apparatus. The recorded signal detector consists of an equalizer 30 and a comparator 32 connected in series, and an integrator 34 connected to a feedback loop of the comparator 32, as shown FIG. 4. The equalizer 30 receives a radio frequency signal RF detected by an optical pickup(not shown) . As shown in FIG. 5, the radio frequency signal RF has a different amplitude depending on a length (e.g., 3T to 11T) of the recording pit 14 or pre-pit 16. Such a radio frequency signal RF is equalized by means of the equalizer 30 in such a manner to has a constant amplitude like an equalized radio frequency signal ERF in FIG. 5. The equalizer 30 controls an amplification factor in accordance with the amplitude of the radio frequency signal RF, thereby applying the equalized radio frequency signal having a constant amplitude to the comparator 32. The comparator 32 converts the equalized radio frequency signal ERF into a pulse signal PS shown in FIG. 5. To this end, the comparator 32 compares the equalized radio frequency signal ERF with a slice voltage Vsl and forms a logical signal from the compared result. The pulse signal generated at the comparator 32 has a width corresponding to a length (e.g., 3T to 11T) of the recording pit 14 or the pre-pit 16. The integrator 34 integrates the pulse signal PS from the comparator 32 to detect an average level voltage of the pulse signal PS, that is, a direct current voltage level. Also, the integrator 34 applies the average level voltage to the comparator 32 as the slice level voltage Vsl. The slice level voltage Vsl varies in accordance with a length of the recording pit 14 and a distance ratio between the recording pits 14. Accordingly, the pulse signal outputted from the comparator 32 always has a duty ratio of 50%, and allows a user data to be reproduced accurately.
As described above, a user data recorded on the disc is encoded in such a manner that a total length of the recording pits 14 included in a constant length of unit recording region (i.e., frame) corresponds to 50% the length of the unit recording region. Accordingly, when a normally recorded user data is reproduced, an average voltage level of the pulse signal PS detected by the integrator 34 has "0 V". As a result, the normal pulse signal PS identical to that upon reproduction is detected from the comparator 32 without a variation in the slice level voltage Vsl. Otherwise, the recording pits occupy a region more than or less than 50%, of the unit recording region at the time of recording a data due to a recording light quantity, a rotation speed or a surrounding temperature, etc. A high logic pulse width of the pulse signal PS when a user data recorded in the unit recording region is reproduced, becomes narrower and wider than a high logic pulse width of the pulse signal PS when a normally recorded data is reproduced. This result from a light quantity reflected by the unit recording region abnormally being larger or smaller than a light quantity reflected by the unit recording region normally. When a unit recording region having the abnormally recorded data is reproduced, an average level voltage detected by the integrator 34 becomes higher or lower than "0 V". As the average level voltage becomes high or low, a high logic pulse width of the pulse signal PS outputted from the comparator 32 becomes narrow or wide. As a result, a pulse signal PS having always a constant range of width (i.e., 3T to 11T) is reconstructed at the comparator 32. As described above, the slice level voltage is controlled in accordance with a duty ratio of the pulse signal PS, thereby stably performing the reconstruction of the pulse signal PS using the comparator 32.
As shown in FIG. 6, a high frequency component of pit train signal PTS from the recording pit train 14 and/or the pre-pit train 16, as well as a low frequency component of wobbling signal WS from the boundary side between the wobbled groove and land tracks 10 and 12, is included in a high frequency signal WRF picked up from the disc such as the above-mentioned DVD-RAM, that is, a high frequency signal picked up from the wobbled track(hereinafter referred to as "wobbling radio frequency signal") . Due to this, a direct current voltage level of the wobbling radio frequency signal PRF fails to have a constant voltage level (e.g., "0 V") and changes in the low frequency component of wobbling signal as shown in FIG. 5. This is caused by a fact that a high frequency component of pit train signal PTS is combined with a low frequency component of wobbling signal WS to swing in accordance with an envelope of the wobbling signal WS. On the other hand, because a high frequency signal NRF, hereinafter referred to as "normal radio frequency signal", picked up from a disc without the wobbled groove and land tracks, hereinafter referred to as "normal disc", does not include the low frequency component of wobbling signal WS, it has a constant direct current voltage level (e.g., "0 V"). When both the wobbling radio frequency signal WRF and the normal radio frequency signal NRF is converted into a shape of pulse signal by means of the recorded signal detector in FIG. 3, a pulse signal WPS, hereinafter referred to as "wobbling pulse signal", derived from the wobbling radio frequency signal WRF has a length different from the length (i.e., 3T to 11T) of the recording pit 14 periodically, whereas a pulse signal NPS, hereinafter referred to as "normal pulse signal", derived from the normal radio frequency signal NRF has a width corresponding to the length of the recording pit 14. In other words, a large or small width of error is periodically generated in the wobbling pulse signal WPS. This is caused by a fact that the large-width error and the small-width error in the wobbling pulse signal WPS is canceled every a period of the wobbling signal WS to maintain a direct current voltage level detected at the integrator 32 constantly. Such a pulse reconstruction error will be more apparent from the following description with reference to FIG. 7.
Referring to FIG. 7, the wobbling radio frequency signal WRF is sliced on a basis of a slice level voltage Vsl to produce a wobbling pulse signal WPS. If the normal radio frequency signal NRF is sliced on a basis of a slice level voltage Vsl, then a normal pulse signal NPS is produced. Edges of the wobbling pulse signal WPS becomes gradually distant from edges of the normal pulse signal NPS and thereafter draws gradually near to them in accordance with a change in the amplitude of the wobbling signal. More specifically, the edges of the wobbling pulse signal WPS is most far away from the edges of the normal pulse signal NPS at the peak of the wobbling signal WS. For example, at the positive peak of the wobbling signal WS, the wobbling pulse signal WPS rises at a time "t1" going by a time interval .DELTA.2 from a time "t1" when the normal pulse signal NPS rises. Further, a deviation .DELTA.2 between the edge of the wobbling pulse signal WPS at the peak of the wobbling signal WS and the edge of the normal pulse signal NPS becomes larger than deviations .DELTA.1 and .DELTA.3 between the edge of the wobbling pulse signal WPS at the rising portion and the falling portion of the wobbling signal WS and the edge of the normal pulse signal NPS. Moreover, a width of the wobbling pulse signal WPS becomes narrower than that of the normal pulse signal NPS at the positive region of the wobbling signal WS, whereas a width of the wobbling pulse signal WPS becomes wider than that of the normal pulse signal NPS at the negative region of the wobbling signal WS.
As described above, the conventional recording signal detector detects a pulse signal having a width different from the length of the recording pits on the wobbled track. Such a width error in the pulse signal acts as a noise component at the later signal processing stage such as the conversion of channel bit stream, thereby preventing a user data on the wobbled track from being reproduced accurately.